The present invention relates to an axial-flow fan.
FIG. 11 and FIG. 12 are an oblique view and a sectional view of a prior-art axial-flow fan, such as the one shown in Japanese Utility Model Application Kokai Publication No. 68477/1987. In the figures, a cylindrical air duct 2 is defined by a frame 1, and a motor support 4 is fixed to the frame 1 by means of legs 3. An electric motor 5 is supported by the motor support 4. A stator 6 is fixed to the motor support 4, while magnets are mounted on the motor support 4 via bearing 7, so that the magnets 8 can rotate, and the magnets 8 confront the stator 6. A blade assembly 10, formed integrally and of synthetic resin is disposed within the air duct 2. The blade assembly 10 comprises a cylindrical boss 10a and blades 10b connected to the cylindrical surface of the boss 10a.
When the stator 6 of the motor 5 is energized, a magnetic flux is generated, and because of the magnetomotive interaction between the rotor 9 and the magnets 8, the blade assembly 10 rotates. As a result, air is taken in from above as seen in FIG. 12, passed through the air duct 2, and blown out toward the bottom as seen in FIG. 12, through the openings between the legs 3.
It will be understood that the legs 3 are in the way of the air stream, and the legs 3 have surfaces normal to the direction of the air stream. Moreover, the air duct 2 is in the form of a cylinder whose side surfaces are formed of straight lines which are also called "generators". Furthermore, the boss 10a of the blade assembly 10 is cylindrical, so that its resistance to air flow is substantial.